Mechanism for the posture-specific plasma volume increase after a single intense exercise protocol

To test the hypothesis that exercise-induced hypervolemia is a posture-depe ndent process, we measured plasma volume, plasma albumin content, and renal function in seven healthy subjects for 22 h after single upright (Up) or s upine (Sup) intense (85% peak oxygen consumption rate) exercise. This postu re was maintained for 5 h after exercise. Plasma volume decreased during ex ercise but returned to control levels by 5 h of recovery in both postures. By 22 h of recovery, plasma volume increased 2.4 +/- 0.8 ml/kg in Up but de creased 2.1 +/- 0.8 ml/kg in Sup. The plasma volume expansion in Up was acc ompanied by an increase in plasma albumin content (0.11 +/- 0.04 g/kg; P < 0.05). Plasma albumin content was unchanged in Sup. Urine volume and sodium clearance were lower in Up than Sup (P < 0.05) by 5 h of recovery. These d ata suggest that increased plasma albumin content contributes to the acute phase of exercise-induced hypervolemia. More importantly, the mechanism by which exercise influences the distribution of albumin between extra- and in travascular stores after exercise is altered by posture and is unknown. We speculate that factors associated with postural changes (e.g., central veno us pressure) modify the increase in plasma albumin content and the plasma v olume expansion after exercise.